A plurality of various types of fuel pumps have been employed to convey liquid fuel from the vehicle's storage tank to the carburetor of an internal combustion engine. Engine-driven mechanical fuel pumps are -- for all practical purposes -- located in proximity to the engine and remote from the fuel storage tank; therefore, a lengthy suction line must be provided from the pump to the tank. Long suction lines require high vacuum to achieve the desired flow rate and therefore subject the fuel to lower pressures resulting in greater vaporization of the fuel which, in turn, causes "vapor lock" under adverse conditions. Electrically powered fuel pumps have the advantage of being installed in, or close to, the fuel storage tank, thus requiring a minimum length of suction line which greatly reduces the possibility of vapor lock.
Another advantage of an electric fuel pump is that it supplies fuel to the carburetor before the engine is cranked, thus providing faster starting under adverse conditions.
Prior to this invention, all electrically powered fuel pumps that are mounted outside the fuel tank must, of necessity, be self-priming. Only positive displacement pumps such as gear, vane, or piston pumps are self-priming. Positive displacement pumps rely upon closely fitted parts in order to effect a suction prime. Because of this, they are subjected to extensive wear and subsequent short life. Furthermore, additional means must be provided to cope with the discharge of a positive displacement pump when the demand is less than the output of the pump. In other words, positive displacement pumps, of themselves, are not demand responsive.
Although centrifugal pumps were used prior to this invention, such applications require in-the-tank installation. In other words, the entire pump was submerged in the fuel. Such applications require specialized fuel tanks and, therefore, are practical only when employed by the original vehicle manufacturer.